Dc offset correction in an antenna aperture

ABSTRACT

A method and apparatus for DC offset correction in an antenna aperture are described. In one embodiment, the antenna comprises: an array of antenna elements having liquid crystal (LC); drive circuitry coupled to the array and having a plurality of drivers, each driver of the plurality of drivers coupled to an antenna element of the array and operable to apply a drive voltage to the antenna element; and voltage correction logic coupled to the drive circuitry adjust drive voltages to compensate for an offset between a first magnitude of a first voltage applied to the LC of each antenna element during a first interval of drive polarity and a second magnitude of a second voltage applied to the LC of said each antenna element during a second interval of drive polarity opposite the drive polarity of the first interval.

PRIORITY

The present patent application claims priority to and incorporates byreference the corresponding provisional patent application Ser. No.62/561,110, titled, “RF RIPPLE CORRECTION,” filed on Sep. 20, 2017 andprovisional patent application Ser. No. 62/564,877, titled, “DC OFFSETCORRECTION IN AN RF TFT ANTENNA APERTURE,” filed on Sep. 28, 2017.

FIELD OF THE INVENTION

Embodiments of the present invention relate to the field of radiofrequency (RF) devices having liquid crystals (LCs); more particularly,embodiments of the present invention relate to the driving and controlof radio frequency (RF) devices having liquid crystals (LCs) for whichRF ripple, flicker or other observations have been made.

BACKGROUND OF THE INVENTION

Display devices using liquid crystals (LC) typically use a drive methodthat inverts the polarity of the drive voltage applied across the LC atregular intervals. These intervals are typically called time frames orframes. This is done to prevent or minimize trapping of charges withinthe LC device that can result in a storage of a voltage within the LCdevice. These charges arise from numerous sources, mostly coming fromcontamination or a degradation of materials in the LC device. Apersistent application of a given polarity separates the charges ofcontaminants (such as organic acids), and moves them to the boundariesof the LC device, where they may stick. By inverting the polarity of theapplied voltage, the separation and transport of these charged speciescan be reduced. However, inverting the voltage symmetrically isdifficult to do, and thus a “net DC offset” results.

A condition called “flicker” can also occur, which is caused when thereis a sufficient difference between the absolute value of the voltageapplied during a positive frame and that applied during a negative framesuch that the optical properties of the LC in positive and negativeframes are different and visible by a human eye. In a display, these maybe seen or detected by a light sensing device. Over time, the asymmetrybetween the positive and negative frames that caused flicker results instorage charge. Stored charge within the device can create differencesbetween the voltage that is intended to be applied to the LC, and thevoltage that is actually applied. This can result in a reduction in theroot mean squared (RMS) voltage applied to the elements. Another symptomof this problem, referred to herein as “image sticking”, can occur,which is an influence of a previously applied image pattern upon thenext image pattern.

Although regularly inverting the polarity of the applied voltage iseffective to prevent charge trapping, this by itself is not sufficientto prevent problems like “flicker”. If there is a sustained differencebetween the applied voltages in the positive polarity and the negativepolarity, this can result in a “net DC offset” between the frames,whereby there is a net accumulation of charges at the boundaries of theLC device over time.

To prevent this in an LC-based device, it is desired that the DC offsetbetween the absolute value of voltage applied to the LC device duringthe one interval of the drive polarity and the absolute value of thevoltage applied during the next interval of opposite drive polarity beas close to zero as possible.

In LC displays, adjustment of the DC offset may be done by compensatingthe voltage value sent to each element for each polarity at every graylevel. In a display, the amount of the compensation voltage at eachpolarity at chosen gray levels may be determined optically and isselected to null the flicker. That is, a voltage difference between thepositive and negative polarity of frames results in an optical flicker,which can be observed by an optical sensor or array of sensors (camera)and nulled using a correction algorithm in an automated test setup.Then, those correction values can be stored and used for minimizing theoffset.

A DC offset problem is described above for LC displays. The samephenomenon is observed in LC RF antenna since LC driving mechanism isthe same as displays. The effect of this phenomenon is observed as RFripple in the antenna performance which degrades the carrier to noise(C/N) ratio at the receiver. DC offset correction methods used in LCdisplays cannot be applied to the current state of the LC RF antennabecause the antenna structure blocks the path for optical measurementsof the LC response.

SUMMARY OF THE INVENTION

A method and apparatus for DC offset correction in an antenna apertureare described. In one embodiment, the antenna comprises: an array ofantenna elements having liquid crystal (LC); drive circuitry coupled tothe array and having a plurality of drivers, each driver of theplurality of drivers coupled to an antenna element of the array andoperable to apply a drive voltage to the antenna element; and voltagecorrection logic coupled to the drive circuitry adjust drive voltages tocompensate for an offset between a first magnitude of a first voltageapplied to the LC of each antenna element during a first interval ofdrive polarity and a second magnitude of a second voltage applied to theLC of said each antenna element during a second interval of drivepolarity opposite the drive polarity of the first interval.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given below and from the accompanying drawings of variousembodiments of the invention, which, however, should not be taken tolimit the invention to the specific embodiments, but are for explanationand understanding only.

FIG. 1 is a block diagram of one embodiment of voltage adjustmentapparatus.

FIG. 2 illustrates the transmission parameter S21 over time withoutradio-frequency (RF) ripple.

FIG. 3 illustrates the transmission parameter S21 over time with RFripple.

FIG. 4 illustrates driving voltages for an RF unit cell in an LC antennaaperture.

FIG. 5 illustrates data (source) driver output control using gammavoltages.

FIG. 6 is a flow diagram of an embodiment of a RF ripple correctionprocess.

FIGS. 7A and 7D illustrate an example of voltage adjustments using oneembodiment of the RF ripple correction process.

FIG. 8 is a flow diagram of another embodiment of a RF ripple correctionprocess.

FIG. 9 illustrates an example of a transmission versus voltage curve.

FIG. 10 is a flow diagram of a one embodiment of a process to determineDC offset correction values.

FIG. 11 illustrates one embodiment of routing for a single teststructure located outside of the waveguide area.

FIG. 12 illustrates one embodiment of a test structure.

FIG. 13 illustrates one example of gate and source line routing foroptically transparent test structures.

FIGS. 14 and 15 illustrate examples of patch glass (substrate) and irisglass (substrate) structures, respectively, that form the patch and irisfor the antenna aperture.

FIGS. 16 and 17 illustrate examples of routing on the patch glasssubstrate and iris glass substrate, respectively.

FIG. 18 illustrates the schematic of one embodiment of a cylindricallyfed holographic radial aperture antenna.

FIG. 19 illustrates a perspective view of one row of antenna elementsthat includes a ground plane and a reconfigurable resonator layer.

FIG. 20 illustrates one embodiment of a tunable resonator/slot.

FIG. 21 illustrates a cross section view of one embodiment of a physicalantenna aperture.

FIGS. 22A-D illustrate one embodiment of the different layers forcreating the slotted array.

FIG. 23 illustrates a side view of one embodiment of a cylindrically fedantenna structure.

FIG. 24 illustrates another embodiment of the antenna system with anoutgoing wave.

FIG. 25 illustrates one embodiment of the placement of matrix drivecircuitry with respect to antenna elements.

FIG. 26 illustrates one embodiment of a TFT package.

FIG. 27 is a block diagram of one embodiment of a communication systemhaving simultaneous transmit and receive paths.

DETAILED DESCRIPTION

In the following description, numerous details are set forth to providea more thorough explanation of the present invention. It will beapparent, however, to one skilled in the art, that the present inventionmay be practiced without these specific details. In other instances,well-known structures and devices are shown in block diagram form,rather than in detail, in order to avoid obscuring the presentinvention.

Overview of Voltage Correction

A method and apparatus for controlling the drive scheme of an antenna isdisclosed. In one embodiment, the antenna comprises a flat panelantenna, such as described, for example, but not limited to, antennaembodiments described below. Note that the techniques described hereinare not limited to such an antenna.

In one embodiment, the drive scheme involves the selection of voltagevalues for controlling antenna elements in an antenna. In oneembodiment, the antenna elements are RF radiating antenna elements;however, the techniques disclosed herein are not limited to such antennaelements. In one embodiment, the RF radiating antenna elements aremetamaterial liquid crystal-based antenna elements. In one embodiment,the metamaterial antenna elements are surface scattering metamaterialantenna elements, such as those, for example, but not limited to, thosedisclosed in more detail below.

In one embodiment, the drive scheme for an antenna is modified based onobservations made with respect to the antenna. The observations may beobtained by test equipment, test structures, and sensors. In oneembodiment, the observations include observations regardingradio-frequency (RF) ripple, flicker, and/or environmental changes(e.g., temperature changes, pressure changes, etc.).

Based on the observations, changes to the drive scheme are made. In oneembodiment, one or more changes to the drive scheme involve adjustingone or more voltages that control the operation of some portion of theantenna. In one embodiment, the adjustment is made to one or more ofgamma voltages, gate, source and/or drain voltages of a transistor(e.g., a thin film transistor (TFT)), a reference, or common, voltage(e.g., Vcom), etc.

In the case of RF ripple and/or flicker observations, the techniquesdisclosed herein adjust voltage values that are specified to controllingantenna elements, including the drivers for such antenna elements. Inone embodiment, gamma voltage values are adjusted. In anotherembodiment, a common voltage, e.g., Vcom, value is adjusted. Note thatthe voltage adjustments are not limited to these voltages.

FIG. 1 is a block diagram of one embodiment of voltage adjustmentapparatus. In one embodiment, the apparatus is part of an antenna. Inanother embodiment, the apparatus is used by the antenna but is separatefrom the antenna. In yet another embodiment, parts of the apparatus aredistributed such that a portion is part of an antenna and another partis separate from but used by an antenna.

Referring to FIG. 1, voltage adjustment component 100 receives one ormore drive/control voltage values 101 (e.g., gamma voltage values, gate,source and/or drain voltages of a transistor (e.g., a thin filmtransistor (TFT)), a reference, or common, voltage (e.g., Vcom), etc.)and observation data 102 related to observations made with respect to anantenna. In one embodiment, observation data 102 comprises one or moreof RF ripple measurements or information, flicker measurements orinformation, environmental measurements, etc. These may be obtained fromtesters, test structures, sensors, etc.

In response to these inputs, voltage adjustment component 100 performsvoltage adjustments to the drive and/or control voltages used by theantenna. In one embodiment, voltage adjustment component 100 performsvoltage adjustments in response to RF ripple that has been observed. Inanother embodiment, voltage adjustment component 100 performs voltageadjustments in response to a flicker that has been observed. In yetanother embodiment, voltage adjustment component 100 performs voltageadjustments in response to RF ripple and flicker that has been observed.

In one embodiment, voltage adjustment component 100 performs voltageadjustments in response to RF ripple that has been observed using an RFripple correction component 100A. In another embodiment, voltageadjustment component 100 performs voltage adjustments in response to aflicker that has been observed using a DC offset correction component100B. In yet another embodiment, voltage adjustment component 100performs voltage adjustments in response to RF ripple and flicker thathas been observed using a combined RF ripple and DC offset correctioncomponent in which RF ripple correction component 100A and DC offsetcorrection component 100B are combined or work in series. In oneembodiment, the two methods are combined such that the optical DC offsetcorrection/detection method (100B) is used to establish expected gammavoltage correction amounts and then a finer correction with RF ripplemethod (100A) is performed around those expected values. The amount ofvoltage correction found using 100B may be different than what's neededfor RF elements in the array if the test structures are placed only inthe periphery or the capacitance of the ITO structure is close butdifferent from RF elements. The combination of two methods can providemore precise correction (100A) in a shorter time (100B), withoutscanning the whole voltage range. In one embodiment, voltage adjustmentcomponent 100 comprises a reference or common voltage Vcom adjustmentcomponent 100C to adjust the common voltage. This adjustment may be madebased on one or more observations (e.g., RF ripple, flicker, etc.).

Voltage adjustment component 100 outputs one or more new, or updated,drive/control voltage values 110 that are stored in memory 103 (e.g., alook up table (LUT)) for access by an antenna controller 104, which usesthe voltage values for use in driving and controlling antenna elementsin an array 105 in a manner well-known in the art.

Examples related to embodiments for ripple correction and DC offsetcorrection performed by voltage adjustment component 100 or used byother antenna embodiments are described in more detail below.

Overview of Ripple Correction

In one embodiment, an LC-based antenna aperture uses a driving schemethat inverts the polarity of the differential voltage applied on theliquid crystal (LC) periodically. The LC-based antenna aperture is, forexample, but not limited to, an antenna aperture described in moredetail below. In one embodiment, the polarity of the LC differentialvoltage is inverted in regular time intervals referred to herein asframes. Voltage polarity inversion is applied to prevent accumulation ofcharges in LC on the electrode surfaces (e.g., patch electrodes in apatch/slot pairs of LC-based antenna elements (e.g., surface scatteringantenna elements described below)). This accumulation causes a buildupof a voltage within the LC layer and interfere with the devicecharacteristics. The inversion of the voltage polarity in each frameprevents that accumulation as it's moving the charges around in eachframe. Those charges are present in the LC mostly due to contaminationor material degradation products. For example, there may be degradationof the LC material that results from exposure to UV in the antennaaperture segment assembly process, reaction of the LC withunintentionally exposed metal, reaction of the LC and alignment layers,etc.

The difference in applied voltage is observed as a difference in opticalproperty of LC between a positive frame and a negative frame. Anothereffect, RF ripple, is observed in the LC antenna aperture when there isa noticeable difference between differential voltage applied on LC in apositive frame and a negative frame. RF ripple in an antenna aperturehaving antenna elements with liquid crystal is analogous to flicker inliquid crystal displays (LCDs). In the LC antenna aperture, thedifference in applied voltage is observed as a difference in the LCdielectric property and eventually the antenna frequency. The differencein the applied differential LC voltage may be due to differences inleakage through transistor or LC, RC delay in the array, cross-talkbetween elements and difference of “kickback” (or feedthrough) voltagebetween positive and negative frames. This difference in antennafrequency causes an antenna response which is varying periodically intime. It can be observed that the center frequency of the antenna, thefrequency where the highest gain is observed, is changing periodically.A testing tool can measure the RF ripple effect.

The RF ripple phenomenon is more clearly observed in time domain,continuous wave (CW) measurements performed at the center frequency. Inan ideal case, the transmission parameter (S21) should be constant overtime as shown in FIG. 2 for one embodiment of an LC-based antennaaperture. When RF ripple is present, a time dependent periodic change inS21 is observed as shown in FIG. 3 for one embodiment of an LC-basedantenna aperture. As previously mentioned, the periodic change inapplied voltage changes the center frequency, which causes a periodicchange in the transmission parameter measured at a constant frequency.

In one embodiment, the voltage correction techniques disclosed hereincorrect for RF ripple in an RF antenna aperture. In one embodiment, inorder to correct for the RF ripple effect, a voltage correction processis used to automate gamma voltage correction, using an RF free spacetest tool, such as, for example, but not limited to the tool disclosedin U.S. application Ser. No. 15/596,370, filed on May 16, 2017 andentitled “Free Space Segment Tester (FSST)”. The automation of gammavoltage correction is used for the purposes of reducing, minimizingand/or eliminating the phenomenon of RF ripple. Note that this processmay be performed one or more times. In one embodiment, the process isrepeated when a significant change has occurred, such as, for example, adrastic environmental change captured using, for example, one or both oftemperature sensors and/or pressures sensors.

In one embodiment, the voltage correction unit performs a voltageadjustment method. In one embodiment, the method reduces, andpotentially minimizes, the RF ripple by readjusting the driving voltagesto apply the same differential voltage in both a positive and a negativeframe. In one embodiment, the voltage adjustment method for RF ripplecorrection is applied in a free space test (FST) measurement system.

In one embodiment, the RF response of the antenna (transmissionparameter S21) is observed in both frequency and time domain. Gammavoltage values are used for creating the “Data” voltages are employed toreadjust the driving voltage. The gamma voltage controls the output“Data” voltage as shown in FIG. 4 for a typical “Data” driver chip.Referring to FIG. 4, the driving voltages for an RF unit cell in an LCantenna aperture include a reference, or common, voltage Vcom 402 thatis coupled to the RF element 412 and storage capacitor 411. RF element412 and storage capacitor 411 are also coupled to the drain oftransistor 410. In one embodiment, transistor 410 is a thin filmtransistor (TFT). Gate 402 of transistor 410 receives a scan voltagefrom a scan/gate driver 420. Data/source 401 of transistor 410 iscoupled to receive the output data voltage from a data driver 421, whichis controlled by a gamma voltage from gamma voltage reference generator422.

The gamma voltage driver “linearizes”/“corrects” the measured power vsvoltage response for the desired frequencies for the segments. For eachgray level/polarity, a new gamma voltage is calculated using the AVcomfound for that gray level/polarity. These values are then placed into alook up table in memory (e.g., an EEPROM) on a controller board. In oneembodiment, timing controller 430 is the controller board. These valuesare used to set up the gamma voltage generator 422. Gamma voltagegenerator 422 inputs into a resistor ladder in data driver 421, with thegamma voltages going to nodes on the resistor ladder. With this gammachip info, and the gray level data from the controller board, datadriver 421 writes the corrected source voltages to each source line asthe “row” (gate) lines scan, thereby updating new information for eachframe.

A timing controller 430 is coupled to control data driver 421 andscan/gate driver 420. In one embodiment, timing controller 430 controlsthe timing of the data voltage driving, as well as spitting data out tothe data driver, which is using the gamma voltage generator to outputthe proper analog voltages to the source lines.

In one embodiment, the data driver chip output is defined at each grayshade level for both a negative and a positive frame. For N gammavoltage levels, there are N/2 gray shade levels directly controlled withgamma voltage. In one embodiment, RF ripple correction is performed atthose N/2 gray shade levels.

In one embodiment, the RF ripple correction is performed by gammavoltage correction logic 423. In one embodiment, gamma voltagecorrection logic 423 comprises circuitry executing software.Alternatively, gamma voltage correction logic 423 comprises hardware,software, firmware or a combination of two or more of these. In oneembodiment, the RF ripple is measured using a free space tester (FST),and gamma voltage correction logic 423 determines the AVcom usingsoftware being executed by circuitry (e.g., a processor, controller,digital logic, etc.), calculates the gamma voltage using the softwareand sends the new gamma voltage values to gamma voltage generator 422using the software.

In one embodiment, an initial set of gamma voltages is determined. FIG.5 illustrates an example of such gamma voltage curves. Referring to FIG.5, the voltage curves are symmetric with respect to a voltage level inthe middle, referred to as hAVDD. In one embodiment, that voltage levelis also used as the initial value for the common voltage (Vcom). In oneembodiment, the highest gray shade is set to achieve the largest voltagerange possible and the lowest gray shade is set to achieve a 0Vdifferential LC voltage.

When gray shade level is set to the largest voltage range, the RFresponse of the LC-based antenna element is observed in FST and the RFripple is measured for the center frequency. If ripple amount is largerthan the criteria, Vcom is increased or decreased until ripple amount isbelow the criteria. At that Vcom value, the center frequency isdetermined again in the frequency domain. The ripple measurement in thetime domain is repeated at the new center frequency. If ripple amount isbelow the criteria, this Vcom value is established as the new Vcom value(Vcom_adj). Otherwise, the Vcom adjustment process is repeated untilripple amount is below the criteria.

The Vcom adjustment process is repeated for the remaining (N/2)−1 grayshade levels with a minor modification. For each of the remaining grayshades, the RF response and center frequency are measured. The rippleamount is measured in the time domain and Vcom is increased or decreasedto match the ripple criteria. In one embodiment, the criterion is athreshold in which RF ripple above the threshold distorts the signal orotherwise affects the carrier to noise (C/N) at the receiver. In oneembodiment, the threshold is set to 0.10 dB. Then RF responsemeasurement is repeated to measure the new center frequency. The rippleis remeasured at the new center frequency. This process is repeateduntil the ripple amount satisfies the criteria. Vcom at this step iscalled Vcom temp.

ΔVcom=Vcom_temp−Vcom_adj

This difference (ΔVcom) is subtracted from the gamma voltage values forthis gray shade level to calculate the new gamma voltage for this grayshade level. There are a number of ways to apply this adjustment. In oneembodiment, ΔVcom is subtracted from both gamma voltage values, relatedto the positive and negative frames, used in that gray shade tocalculate the new gamma voltage values for this gray shade level. Inanother embodiment, 2*ΔVcom is subtracted from one of the gamma voltagevalues in that gray shade.

In one embodiment, the Vcom level is set prior to the RF ripplecorrection and only temporary Vcom readjustment is allowed. Then, thegamma voltage adjustment described in the previous paragraph is alsoused for the highest gray shade level.

This adjustment process is repeated for the remaining gray shade levelsto calculate ΔVcom and updated gamma voltage values. In one embodiment,the updated gamma voltage set is used with Vcom_adj as the new Vcomlevel to measure the ripple amount again at new center frequency foreach gray shade level to confirm the ripple criteria. If the measuredripple amount satisfies the ripple criteria, the RF ripple correctionprocess is considered as complete. Otherwise, the gamma voltageadjustment process is repeated until the RF ripple criteria aresatisfied.

FIG. 6 illustrates one embodiment of a flow diagram of the above RFripple correction process performed as part of one embodiment of an RFripple correction unit. The process is performed by processing logicthat may comprise hardware, software, firmware, or a combination of thethree.

FIGS. 7A-7D illustrate one embodiment of a voltage adjustment processfor a pseudo half Vdd drive mode for an antenna. Referring to FIG. 7A,the Vsource voltage is between 0V-7V along with the Vcom voltage. Thisis referred to herein as a 7V Half Vdd (True Half Vdd) driving mode. Insuch a case, the LC voltage (e.g., the voltage on the patch of apatch/slot antenna element) will be between 7V and −7V for the positiveand negative frames. This represents the ideal case where the twovoltages are symmetric about 0V.

FIG. 7B illustrates the situation where two voltage levels are notsymmetric about a voltage. Referring to FIG. 7B, the voltage on thesource, Vsource, is between 0V and 6.5V and the range of the voltage isbetween 6.5V and −7V. This results in RF ripple. To address this, the RFcorrection unit increases the common voltage Vcom (as shown in FIG. 7C)or decreases Vcom (as shown in FIG. 7D). After increasing Vcom as shownin FIG. 7C, ripple is measured and if it is determined that RF rippleincreases, the RF ripple correction unit determines that the voltageadjustment is going in the wrong direction moves to adjust Vcom bydecreasing it. If the results of decreasing Vcom causes a reduction inripple, then the RF ripple correction unit continues to decrease Vcomuntil RF ripple no longer decreases. Note that Vcom may be increased ifthe decreasing Vcom results in an increase in RF ripple.

In one embodiment, the step size used in adjusting Vcom may be the samethroughout the RF ripple correction process. In another embodiment, thestep size used in adjusting Vcom may change throughout the RF ripplecorrection process. For example, the step size may initially be uniform;however, as the amount of ripple has been decreasing (e.g., due toadjusting Vcom downward) and suddenly increases as a result of anadjustment in Vcom, the size of the adjustment may be made smaller inthe opposite direction (e.g., an adjustment in Vcom upward) as theprocess of identifying a Vcom that results in no RF ripple or apredetermined amount of RF ripple (e.g., RF ripple being under apredetermined level) has been obtained.

A defined RF ripple correction process can be used for adjustment ofgamma voltages on each segment of an antenna aperture (where thesegments are coupled together to form a single aperture). In oneembodiment, RF ripple correction process calculates an appropriate gammavoltage set using adjustment results on a small number of samples fromeach lot/batch of antenna elements being evaluated.

Note that one alternative antenna driving mode to the driving mode shownin FIGS. 7A-7D is referred to herein as 9V Half Vdd (Pseudo Half Vdd)driving mode. An important difference between 9V Half Vdd (Pseudo HalfVdd) and 7V Half Vdd (True Half Vdd) driving modes is that Vcom isswitching between VcomH and VcomL in 9V mode and Vcom is a constantvoltage in 7V mode.

FIG. 8 is a flow diagram of another embodiment of a RF ripple correctionprocess. The process is performed by processing logic that may comprisehardware, software, firmware, or a combination of the three. In oneembodiment, operations set forth in FIG. 8 are performed by an RF ripplecorrection unit.

Referring to FIG. 8, the process begins by processing logic checkingwhether adjustment of Vcom is allowed (processing block 801). If it'sallowed, then the process transitions to processing block 802. If not,the process transitions to processing block 804.

At processing block 802, processing logic generates initial gammavoltages for a symmetric voltage curve for positive and negative frames.The highest and lowest gamma voltage values are typically determined bydriving chip specifications.

At processing block 802, processing logic also determines an initialVcom value as the close as possible to generate 0V on the LC for thelowest gray shade level.

Thereafter, processing logic goes to highest gray shade level,corresponding to highest and lowest gamma voltages, and readjusts Vcomto meet ripple criteria (processing block 803A). In one embodiment, aspart of processing block 803A, processing logic readjusts Vcom, checksthe new center frequency (CF), checks the ripple at the new CF,readjusts Vcom, and if needed, repeats checking the center frequency andripple.

After readjusting Vcom, processing logic replaces the initial Vcom valuefor the rest of the measurement with the adjusted Vcom (Vcom_adj) value.Thereafter, the process transitions to processing block 806A.

At processing block 804, processing logic generates the initial gammavoltages for a symmetric voltage curve for positive and negative framesaround Vcom. As discussed above, in one embodiment, the highest andlowest gamma voltage values are typically determined by driving chipspecifications. In one embodiment, processing logic sets gamma voltagesin the middle of the highest and lowest gamma voltage values as close aspossible to generate 0V on LC for the lowest gray shade level.

Next, processing logic goes to the highest gray shade level, measuresripple and readjusts Vcom (processing block 805B). In one embodiment,processing logic checks the new center frequency (CF) and checks theripple at the new CF. In one embodiment, only a temporary Vcom change isallowed, and the nominal Vcom is referred to as Vcom_adj. In oneembodiment, Vcom is temporarily readjusted to meet ripple criteria. ThatVcom value is referred to as Vcom_temp.

After measuring ripple, processing readjusts Vcom again if the rippledoesn't meet the criteria and repeats checking and updating Vcom_temp.If ripple criteria are met, processing logic calculates

ΔVcom=Vcom_temp−Vcom_adj

In one embodiment, processing logic calculates new gamma voltages byusing:

gamma_positive_new=gamma_positive−2*ΔVcom

Then processing logic goes to the next gray shade level, measures ripplewith Vcom_adj and readjusts Vcom (processing block 806B). In oneembodiment, processing logic checks the new center frequency (CF) andchecks the ripple at the new CF. Temporarily readjust Vcom to meet theripple criteria. This Vcom value is referred to herein as Vcom_temp. TheVcom is again readjusted if the ripple doesn't meet the criteria, andprocessing logic repeats checking and updates Vcom_temp.

If ripple criteria are met, processing logic calculates

ΔVcom=Vcom_temp−Vcom_adj

In one embodiment, processing logic calculates new gamma voltages byusing one of the following:

gamma_positive_new=gamma_positive−ΔVcom, and

gamma_negative_new=gamma_negative−ΔVcom

Note that in one embodiment, the difference is applied only on one side:

gamma_(positive or negative)_new=gamma_(positive or negative)−2*ΔVcom

After handling the current gray shade level, processing logic changesthe Vcom value back to its initial value (processing block 806C) and theprocess transitions to processing block 807.

The steps above from FIG. 8 are for the gamma voltage correction in atrue half Vdd mode where Vcom is not switching. For a different drivemode, pseudo half Vdd, where Vcom is switching between Vcom High andVcom Low levels as seen in FIGS. 7A-7D, the process of FIG. 8 can bemodified so that RF ripple correction is performed by changing Vcom Highand Vcom Low levels until the RF ripple is below the threshold. In thatcase, in one embodiment, new gamma voltages are calculated according tothe following:

gamma_positive_new=gamma_positive−(Vcom_low_temp−Vcom_low_adj)

gamma_negative_new=gamma_negative−(Vcom_high_temp−Vcom_high_adj)

Vcom_high_adj and Vcom_low_adj, similar to Vcom_adj, are Vcom High/Lowlevels obtained in the adjustment step. Vcom_high_temp andVcom_low_temp, similar to Vcom_temp, are temporary Vcom High/Low levelsused in RF ripple correction step. In the other case, process describedin FIG. 8 can be applied without any change if the same amount of Vcomchange is applied to both Vcom High and Vcom Low level.

At processing block 807, processing logic checks whether all gray shadelevels have been completed. If not, the process transitions toprocessing block 806A and the process continues there for the remaininggray shade levels. If all the gray shade levels have been completed,processing transitions to processing block 808.

After all remaining gray shade level have been evaluated, and correctedif necessary, processing logic updates a gamma voltage table thatcontains the gamma voltages for the gray shade levels with new values(processing block 808).

In one embodiment, processing logic repeats the RF ripple measurement(processing block 809) and check whether the RF ripple criteria is met(processing block 810). If it isn't met, then repeat, then the processtransitions to processing block 805A for gray shade levels not meetingthe criteria, and the process repeats from there until the criteria ismet for all gray shade levels. If the criteria are met (processing block810), then the process ends.

Overview of DC Offset Correction

Embodiments of the invention include a technique to correct for directcurrent (DC) offsets in an RF antenna aperture. There are many factorsthat can contribute to a net DC offset in an antenna. The chargingratios, kickback voltages, and charge leakages are typically not equalbetween positive and negative frames, and additionally, these values maychange with gray level.

There are several difficulties in applying display methods for handlinga DC offset to an RF TFT aperture. For example, one difficulty is thatthere are optically opaque metal layers that prevent observation of theLC in the critical areas of the elements.

Embodiments of the invention include structures and methods foroptically observing flicker in selected places in the RF TFT aperture,to enable using a correction technique to reduce the DC offset in RF TFTapertures. Embodiments of the invention take advantage of the fact that,besides having an anisotropy in permittivity to RF radiation, the liquidcrystals used to build RF TFT apertures also have an optical anisotropymeasured by the difference between the index of refraction of the fast(short) and slow (long) axis of the LC molecules.

Typically, the delta n of LC used for RF TFT aperture purposes is largerthan the delta n of an LC whose properties have been optimized for adisplay. Between crossed polarizers with rubbing direction at 45 degreesto the polarizers, at an LC gap of 2.7 um, the electro-optic curve of anRF optimized LC will show several maxima and minima from 0 to 7.5 Vrms.

FIG. 9 illustrates an example of a transmission versus voltage curve.Referring to FIG. 9, as a consequence of the LC being optimized for RFantenna use, the optical delta n of this LC is much larger than in an LCoptimized for an LCD. For an electrically controlled birefringence (ECB)cell with the proper choice of polarizers and rubbing direction, thetransmission versus voltage curve would look something like the plot inFIG. 9.

An optical transmission difference between the positive and negativeframes are accentuated in parts of the optical transmission curve wherethe change in transmission with voltage is rapid (steep slope). Thoseregions should be used for determining correction voltages for graylevels.

For given positive and negative frames of an RF TFT aperture gray level,there will be corresponding optical states for the positive and negativeframes on the electro-optic curve. These corresponding optical states onthe electro-optic curve will be different due to the DC offset. Thisdifference between optical transmission values will be observed as a“flicker”. In one embodiment, these optical states for the positive andnegative frames on the electro-optic curve are used to correct the DCoffset. The DC offset correction techniques disclosed herein generate aDC offset correction voltage that can be determined by nulling the“flicker”.

In one embodiment, the net DC offset is adjusted by adjusting the Vcomvoltage. This may be for different driving modes. For example, in oneembodiment, at a gross level, for a ½ VDD mode of driving (in which thevoltage range between the positive and negative frames is ½ VDD), thenet DC offset is adjusted by adjusting the Vcom voltage. In oneembodiment, the DC offset correction is performed by DC offsetcorrection logic. In one embodiment, such logic comprises circuitryexecuting software and is coupled to circuitry such as shown in FIG. 4to adjust the Vcom voltage. Alternatively, DC offset correction logiccomprises hardware, software, firmware or a combination of two or moreof these.

In one embodiment of a process, it is desirable to reduce the frame rate(lengthen the frame time) to increase the time the LC has to respond tothe voltages of the positive and negative frames. This is because LC hasa response time and one needs to wait for that response time to observethe optical response to voltage change. If the frame time isn't longenough to observe the LC response, the frame time used during DC offsetcalibration can be increased. However, the frame rate cannot be simplylengthened because the length of the frame time may affect keycomponents of the DC offset, such as, for example, the charging ratioand voltage leakage. In one embodiment, increasing the time the LC hasto respond to the voltages of the positive and negative frames isaccomplished by a drive mode where the frame times are kept at the samelength, but multiple frames of positive voltage are written in a row,followed by an equal number of negative frames, and so on, until thenull measurement is completed. In one embodiment, the DC offsetcalibration is performed with that increased frame time but the initialframe time is still used for the antenna operation.

FIG. 10 is a flow diagram of a one embodiment of a process to determineDC offset correction values. The process is performed by processinglogic that may comprise hardware, software, firmware, or a combinationof the three. In one embodiment, operations set forth in FIG. 8 areperformed by DC offset correction logic or a DC offset correction unit.In one embodiment, the DC offset correction unit or logic is in atesting and calibration equipment used in the production line of anantenna.

The process of FIG. 10 relies on observations related to the differencein optical transmission between the positive and negative frames. In oneembodiment, the optical transmission in the positive and negative framesis captured using optical structures. In one embodiment, these opticalstructures are also used to test functionality of matrix row and columndrivers for RF radiating antenna elements (e.g., surface scatteringmetamaterial antenna elements, such as, for example, described below).

Referring to FIG. 10, the process for obtaining correction values beginsby processing logic driving the TFT/window test element at a gray level(processing block 1001) and observing the difference in opticaltransmission between the positive and negative frames (processing block1002).

Processing logic then nulls the flicker between frames by adjusting Vcom(processing block 1003).

After adjusting Vcom to a level that nulls the flicker, processing logicconverts the Vcom value to adjusted positive frame voltage Vpos andnegative frame voltage Vneg (processing block 1004).

Then processing logic applies the adjusted voltage to positive andnegative frames (processing block 1005) and checks for flicker(processing block 1006).

If there is no flicker, processing logic stores adjusted positive andnegative frame voltages in correction look up table (processing block1007).

If flicker still occurs, in one embodiment, the process transitions backto processing block 1003 and the process repeats.

After flicker has been nulled for the gray level, processing logic movesto the next gray level and the process repeats (processing block 1008).

In one embodiment, within each of the gray levels, the process isperformed to null flicker for one element and after the process iscompleted for that element, the process moves to the next element andrepeats until all the elements are tested.

In one embodiment, the corrections determined for RF TFT elements thatwere measured are used to determine corrections of unmeasured RF TFTelements. In one embodiment, the DC offset correction unit interpolatesthe corrections for measured TFT/window test elements to unmeasured RFTFT elements. These unmeasured RF TFT elements may be located betweenthe tested RF TFT elements and/or near the tested RF TFT elements.

Optically Transparent Test Structures to Correct DC Offset

In one embodiment, optically transparent test structures are used toobserve flicker and determine the DC offset to null the flicker. In oneembodiment, these structures are located outside of the RF TFT elementarray and contain equivalent circuits the same or very similar as thosefound in the RF TFT aperture array in the aperture segment. Antennasegments are combined to form the entire antenna array. For moreinformation on antenna segments, see U.S. Pat. No. 9,887,455, entitled“Aperture Segmentation of a Cylindrical Feed Antenna”. In oneembodiment, the optical characteristics of such structures are used toestimate and create correction values to reduce the DC offset in RFelement array.

In one embodiment, the Gate 0 and Source 0 lines associated withvoltages for the test structure are added outside of the waveguideregion (e.g., a waveguide of FIG. 23 of the aperture where additionalholes in the waveguide do not impact performance. FIG. 11 illustratesone embodiment of routing for a single test structure located outside ofthe waveguide area. Referring to FIG. 11, Gate 0, Source 0 and Vcomrouting for voltages for the test structure are shown outside of thearea the waveguide.

FIG. 12 illustrates one embodiment of a test structure. In oneembodiment, the equivalent circuit of the test structure is designed tohave the equivalent circuit of an RF element in the array. Inparticular, the capacitance of the device at the drain is sized to matchthe capacitance of the overlap of a patch element with the iris element.In one embodiment, an optically transparent conductor layer, such as,but not limited to, indium-tin-oxide (ITO), is used as an electrode onboth sides of that capacitor. Observation windows are created in metallayers for optical response of the LC.

Referring to FIG. 12, TFT box 1252 includes a TFT and storage cap, suchas, for example, but not limited to, FIG. 4. Gate metal 1251 is for thegate voltage of the TFT, source 1254 is for the source voltage of theTFT and drain 1255 is for the drain voltage of the TFT that is coupledto a test antenna element (e.g., a surface scattering metamaterialantenna element). In one embodiment, the gate and source are coupled toGate 0 and Source 0 of FIG. 11. The routing 1253 for Vcom is also showncoupled to the TFT 1252.

As shown, a hole 1258 in the iris metal is used as a window to viewflicker using ITO 1256 on the iris (slot) substrate and ITO 1257 on thepatch substrate, such as the patch and iris substrates described in moredetail below.

As discussed above, Gate 0 and Source 0 lines for the test structure arealso added outside the waveguide region of the aperture. In thisembodiment, Gate 0 lines cross all of the source lines as the sourcelines cross from the source driver outside of the aperture segment tothe inside of the segment (e.g., inside being the inside the border sealwhere the LC resides.)

In another embodiment, the Gate 0 can be extended to cross all of theSource lines, and the Source 0 can be extended to cross all of the Gatelines. Optically transparent test structures can be created where Gate 0crosses the source lines and Source 0 crosses the gate lines

FIG. 13 illustrates one example of gate and source line routing foroptically transparent test structures. In one embodiment, the routing ismoved as far as possible outside of the waveguide region and spacescreated in the fan out for TFT/window test elements. In one embodiment,a TFT/window test structure similar to the one shown in FIG. 12 isplaced at each source/Gate 0 junction, where the source could be Source0, Source 1, . . . Source N (source of the last test transistor).

Referring to FIG. 13, gate driver 1301 provides the gate voltages forGates 0-N and source driver 1302 provides the source voltage for Sources0-N, where N designates the last of the gates and sources, respectively.In one embodiment, gate driver 1301 and source driver 1302 are at theedge of the antenna aperture segment.

FIGS. 14 and 15 illustrate examples of patch glass (substrate) and irisglass (substrate) structures, respectively, that form the patch and irisfor the antenna aperture. An example of the glass and iris substratesare described in greater detail below.

Referring to FIG. 14, patch glass substrate 1470 for an antenna aperturesegment includes antenna element aperture boundary 1471 that representsthe boundary of the antenna element array (with antenna elements to theleft of boundary 1471). On the right of boundary 1471 are opticallytransparent test structures (e.g., ITO holes, or windows) withassociated TFTs (and storage capacitor) and the source, gate, and Vcomrouting for those structures.

Referring to FIG. 15, illustrates iris glass substrate 1501 with a ringof holes 1502 in the iris metal layer corresponding to the ITO drains onthe patch glass substrate. ITO pads 1503 over openings in the iris metallayer correspond to the ITO on the patch glass substrate ITO isconnected to Vcom.

In one embodiment, the DC offset in the RF element waveform is opticallynulled in these structures and the resulting “null” values are used toset Vcom and correct the DC offset in RF elements in the array.

In addition to being used to correct the aperture drive for DC offset,in one embodiment, these structures are also used to test thefunctionality of the source and gate drivers at the beginning of thearray via an optical mechanism.

Likewise, in one embodiment, a Source 0 is routed to cross the gatelines as they enter the segment.

In one embodiment, the gate routing is moved and spaces are created toplace a TFT/window test element at each Gate/Source 0 junction. FIGS. 16and 17 illustrate examples of this routing on the patch glass substrateand iris glass substrate, respectively.

Referring to FIG. 16, patch glass substrate 1601 includes an antennaelement aperture 1602 with an antenna aperture boundary 1603. Teststructures 1604 with their TFT (with storage capacitor) and their ITOhole (window) are coupled to gate driver 1605 and source driver 1606.Gate and Vcom routing continue from test structures 1604 into antennaelement aperture 1602.

Referring to FIG. 17, iris glass substrate 1701 is shown with a ring ofwindows (openings) 1703 in the iris metal layer (corresponding to ITOdrains on the patch glass substrate) with ITO pads 1704 over the irismetal openings. Pads 1704 are connected to Vcom.

In one embodiment, the DC offset in the RF element waveform is opticallynulled in these structures and the resulting “null” values used to setVcom and correct the DC offset in RF elements in the array.

Besides being used to correct the aperture drive for DC offset, in oneembodiment, these structures are also used to test the functionality ofthe source and gate drivers at the beginning of the array by an opticalmechanism.

Note that the optically transparent test structures are not limited tobeing outside the antenna element array. In one embodiment, theTFT/optical window test element replaces some RF TFT elements in theantenna array. Due to the holographic nature of forming a beam, anaperture with some small number of elements missing can form beams witha negligible decrease in performance compared to antennas with fullyfunctioning RF element arrays. In one embodiment, RF elements in certainlocations are replaced with TFT/window test elements. In anotherembodiment, the voltage values used to optically null these theTFT/window test elements are used to create a mapping of corrections,which is used to interpolate correction values for the RF element array.In one embodiment, this mapping is stored in a look up table.

In another embodiment, these TFT/window test elements are not placed inthe RF element array according to their geometric position, but areplaced according to their position as an equivalent circuit of thearray. In one embodiment, the “first” and “last” elements, for example,in frame inversion, the first scanned and last scanned, will not havethe same bias over the TFT for the same lengths of time. The RC timeconstant to the TFT is not the same, etc. Some places may be more highlycontaminated (fill opening). Therefore, the DC offset may be differentin these places. In this case, the placement location is the locationfrom an electronic point of view and not a geometric point of view. Thismight mean an element of the first source and first gate line, anelement of the first source and the last gate lines, an element of thelast source and first gate, an element of the last source and last gate,etc.

Furthermore, while the above testing for flicker is described in termsof a transmission LC mode, the techniques described herein are notlimited to such a mode. In another embodiment, the LC optical responseis observed using a reflective LC mode instead of a transmissive LCmode.

Examples of Antenna Embodiments

The RF ripple correction, DC offset correction and voltage adjustmenttechniques described above may be used in a number of antennaembodiments, including, but not limited to, flat panel antennas.Embodiments of such flat panel antennas are disclosed. The flat panelantennas include one or more arrays of antenna elements on an antennaaperture. In one embodiment, the antenna elements comprise liquidcrystal cells. In one embodiment, the flat panel antenna is acylindrically fed antenna that includes matrix drive circuitry touniquely address and drive each of the antenna elements that are notplaced in rows and columns. In one embodiment, the elements are placedin rings.

In one embodiment, the antenna aperture having the one or more arrays ofantenna elements is comprised of multiple segments coupled together.When coupled together, the combination of the segments form closedconcentric rings of antenna elements. In one embodiment, the concentricrings are concentric with respect to the antenna feed.

Examples of Antenna Systems

In one embodiment, the flat panel antenna is part of a metamaterialantenna system. Embodiments of a metamaterial antenna system forcommunications satellite earth stations are described. In oneembodiment, the antenna system is a component or subsystem of asatellite earth station (ES) operating on a mobile platform (e.g.,aeronautical, maritime, land, etc.) that operates using either Ka-bandfrequencies or Ku-band frequencies for civil commercial satellitecommunications. Note that embodiments of the antenna system also can beused in earth stations that are not on mobile platforms (e.g., fixed ortransportable earth stations).

In one embodiment, the antenna system uses surface scatteringmetamaterial technology to form and steer transmit and receive beamsthrough separate antennas. In one embodiment, the antenna systems areanalog systems, in contrast to antenna systems that employ digitalsignal processing to electrically form and steer beams (such as phasedarray antennas).

In one embodiment, the antenna system is comprised of three functionalsubsystems: (1) a wave guiding structure consisting of a cylindricalwave feed architecture; (2) an array of wave scattering metamaterialunit cells that are part of antenna elements; and (3) a controlstructure to command formation of an adjustable radiation field (beam)from the metamaterial scattering elements using holographic principles.

Antenna Elements

FIG. 18 illustrates the schematic of one embodiment of a cylindricallyfed holographic radial aperture antenna. Referring to FIG. 18, theantenna aperture has one or more arrays 654 of antenna elements 653 thatare placed in concentric rings around an input feed 652 of thecylindrically fed antenna. In one embodiment, antenna elements 653 areradio frequency (RF) resonators that radiate RF energy. In oneembodiment, antenna elements 653 comprise both Rx and Tx irises that areinterleaved and distributed on the whole surface of the antennaaperture. Examples of such antenna elements are described in greaterdetail below. Note that the RF resonators described herein may be usedin antennas that do not include a cylindrical feed.

In one embodiment, the antenna includes a coaxial feed that is used toprovide a cylindrical wave feed via input feed 652. In one embodiment,the cylindrical wave feed architecture feeds the antenna from a centralpoint with an excitation that spreads outward in a cylindrical mannerfrom the feed point. That is, a cylindrically fed antenna creates anoutward travelling concentric feed wave. Even so, the shape of thecylindrical feed antenna around the cylindrical feed can be circular,square or any shape. In another embodiment, a cylindrically fed antennacreates an inward travelling feed wave. In such a case, the feed wavemost naturally comes from a circular structure.

In one embodiment, antenna elements 653 comprise irises and the apertureantenna of FIG. 18 is used to generate a main beam shaped by usingexcitation from a cylindrical feed wave for radiating irises throughtunable liquid crystal (LC) material. In one embodiment, the antenna canbe excited to radiate a horizontally or vertically polarized electricfield at desired scan angles.

In one embodiment, the antenna elements comprise a group of patchantennas. This group of patch antennas comprises an array of scatteringmetamaterial elements. In one embodiment, each scattering element in theantenna system is part of a unit cell that consists of a lowerconductor, a dielectric substrate and an upper conductor that embeds acomplementary electric inductive-capacitive resonator (“complementaryelectric LC” or “CELC”) that is etched in or deposited onto the upperconductor. As would be understood by those skilled in the art, LC in thecontext of CELC refers to inductance-capacitance, as opposed to liquidcrystal.

In one embodiment, a liquid crystal (LC) is disposed in the gap aroundthe scattering element. This LC is driven by the direct driveembodiments described above. In one embodiment, liquid crystal isencapsulated in each unit cell and separates the lower conductorassociated with a slot from an upper conductor associated with itspatch. Liquid crystal has a permittivity that is a function of theorientation of the molecules comprising the liquid crystal, and theorientation of the molecules (and thus the permittivity) can becontrolled by adjusting the bias voltage across the liquid crystal.Using this property, in one embodiment, the liquid crystal integrates anon/off switch for the transmission of energy from the guided wave to theCELC. When switched on, the CELC emits an electromagnetic wave like anelectrically small dipole antenna. Note that the teachings herein arenot limited to having a liquid crystal that operates in a binary fashionwith respect to energy transmission.

In one embodiment, the feed geometry of this antenna system allows theantenna elements to be positioned at forty-five-degree (45°) angles tothe vector of the wave in the wave feed. Note that other positions maybe used (e.g., at 40° angles). This position of the elements enablescontrol of the free space wave received by or transmitted/radiated fromthe elements. In one embodiment, the antenna elements are arranged withan inter-element spacing that is less than a free-space wavelength ofthe operating frequency of the antenna. For example, if there are fourscattering elements per wavelength, the elements in the 30 GHz transmitantenna will be approximately 2.5 mm (i.e., ¼ the 10 mm free-spacewavelength of 30 GHz).

In one embodiment, the two sets of elements are perpendicular to eachother and simultaneously have equal amplitude excitation if controlledto the same tuning state. Rotating them +/−45 degrees relative to thefeed wave excitation achieves both desired features at once. Rotatingone set 0 degrees and the other 90 degrees would achieve theperpendicular goal, but not the equal amplitude excitation goal. Notethat 0 and 90 degrees may be used to achieve isolation when feeding thearray of antenna elements in a single structure from two sides.

The amount of radiated power from each unit cell is controlled byapplying a voltage to the patch (potential across the LC channel) usinga controller. Traces to each patch are used to provide the voltage tothe patch antenna. The voltage is used to tune or detune the capacitanceand thus the resonance frequency of individual elements to effectuatebeam forming. The voltage required is dependent on the liquid crystalmixture being used. The voltage tuning characteristic of liquid crystalmixtures is mainly described by a threshold voltage at which the liquidcrystal starts to be affected by the voltage and the saturation voltage,above which an increase of the voltage does not cause major tuning inliquid crystal. These two characteristic parameters can change fordifferent liquid crystal mixtures.

In one embodiment, as discussed above, a matrix drive is used to applyvoltage to the patches in order to drive each cell separately from allthe other cells without having a separate connection for each cell(direct drive). Because of the high density of elements, the matrixdrive is an efficient way to address each cell individually.

In one embodiment, the control structure for the antenna system has 2main components: the antenna array controller, which includes driveelectronics, for the antenna system, is below the wave scatteringstructure, while the matrix drive switching array is interspersedthroughout the radiating RF array in such a way as to not interfere withthe radiation. In one embodiment, the drive electronics for the antennasystem comprise commercial off-the shelf LCD controls used in commercialtelevision appliances that adjust the bias voltage for each scatteringelement by adjusting the amplitude or duty cycle of an AC bias signal tothat element.

In one embodiment, the antenna array controller also contains amicroprocessor executing the software. The control structure may alsoincorporate sensors (e.g., a GPS receiver, a three-axis compass, a3-axis accelerometer, 3-axis gyro, 3-axis magnetometer, etc.) to providelocation and orientation information to the processor. The location andorientation information may be provided to the processor by othersystems in the earth station and/or may not be part of the antennasystem.

More specifically, the antenna array controller controls which elementsare turned off and those elements turned on and at which phase andamplitude level at the frequency of operation. The elements areselectively detuned for frequency operation by voltage application.

For transmission, a controller supplies an array of voltage signals tothe RF patches to create a modulation, or control pattern. The controlpattern causes the elements to be turned to different states. In oneembodiment, multistate control is used in which various elements areturned on and off to varying levels, further approximating a sinusoidalcontrol pattern, as opposed to a square wave (i.e., a sinusoid grayshade modulation pattern). In one embodiment, some elements radiate morestrongly than others, rather than some elements radiate and some do not.Variable radiation is achieved by applying specific voltage levels,which adjusts the liquid crystal permittivity to varying amounts,thereby detuning elements variably and causing some elements to radiatemore than others.

The generation of a focused beam by the metamaterial array of elementscan be explained by the phenomenon of constructive and destructiveinterference. Individual electromagnetic waves sum up (constructiveinterference) if they have the same phase when they meet in free spaceand waves cancel each other (destructive interference) if they are inopposite phase when they meet in free space. If the slots in a slottedantenna are positioned so that each successive slot is positioned at adifferent distance from the excitation point of the guided wave, thescattered wave from that element will have a different phase than thescattered wave of the previous slot. If the slots are spaced one quarterof a guided wavelength apart, each slot will scatter a wave with a onefourth phase delay from the previous slot.

Using the array, the number of patterns of constructive and destructiveinterference that can be produced can be increased so that beams can bepointed theoretically in any direction plus or minus ninety degrees(90°) from the bore sight of the antenna array, using the principles ofholography. Thus, by controlling which metamaterial unit cells areturned on or off (i.e., by changing the pattern of which cells areturned on and which cells are turned off), a different pattern ofconstructive and destructive interference can be produced, and theantenna can change the direction of the main beam. The time required toturn the unit cells on and off dictates the speed at which the beam canbe switched from one location to another location.

In one embodiment, the antenna system produces one steerable beam forthe uplink antenna and one steerable beam for the downlink antenna. Inone embodiment, the antenna system uses metamaterial technology toreceive beams and to decode signals from the satellite and to formtransmit beams that are directed toward the satellite. In oneembodiment, the antenna systems are analog systems, in contrast toantenna systems that employ digital signal processing to electricallyform and steer beams (such as phased array antennas). In one embodiment,the antenna system is considered a “surface” antenna that is planar andrelatively low profile, especially when compared to conventionalsatellite dish receivers.

FIG. 19 illustrates a perspective view of one row of antenna elementsthat includes a ground plane and a reconfigurable resonator layer.Reconfigurable resonator layer 1230 includes an array of tunable slots1210. The array of tunable slots 1210 can be configured to point theantenna in a desired direction. Each of the tunable slots can betuned/adjusted by varying a voltage across the liquid crystal.

Control module 1280 is coupled to reconfigurable resonator layer 1230 tomodulate the array of tunable slots 1210 by varying the voltage acrossthe liquid crystal in FIG. 20. Control module 1280 may include a FieldProgrammable Gate Array (“FPGA”), a microprocessor, a controller,System-on-a-Chip (SoC), or other processing logic. In one embodiment,control module 1280 includes logic circuitry (e.g., multiplexer) todrive the array of tunable slots 1210. In one embodiment, control module1280 receives data that includes specifications for a holographicdiffraction pattern to be driven onto the array of tunable slots 1210.The holographic diffraction patterns may be generated in response to aspatial relationship between the antenna and a satellite so that theholographic diffraction pattern steers the downlink beams (and uplinkbeam if the antenna system performs transmit) in the appropriatedirection for communication. Although not drawn in each figure, acontrol module similar to control module 1280 may drive each array oftunable slots described in the figures of the disclosure.

Radio Frequency (“RF”) holography is also possible using analogoustechniques where a desired RF beam can be generated when an RF referencebeam encounters an RF holographic diffraction pattern. In the case ofsatellite communications, the reference beam is in the form of a feedwave, such as feed wave 1205 (approximately 20 GHz in some embodiments).To transform a feed wave into a radiated beam (either for transmittingor receiving purposes), an interference pattern is calculated betweenthe desired RF beam (the object beam) and the feed wave (the referencebeam). The interference pattern is driven onto the array of tunableslots 1210 as a diffraction pattern so that the feed wave is “steered”into the desired RF beam (having the desired shape and direction). Inother words, the feed wave encountering the holographic diffractionpattern “reconstructs” the object beam, which is formed according todesign requirements of the communication system. The holographicdiffraction pattern contains the excitation of each element and iscalculated by w_(hologram)=w_(in)*w_(out), with w_(in) as the waveequation in the waveguide and w_(out) the wave equation on the outgoingwave.

FIG. 20 illustrates one embodiment of a tunable resonator/slot 1210.Tunable slot 1210 includes an iris/slot 1212, a radiating patch 1211,and liquid crystal 1213 disposed between iris 1212 and patch 1211. Inone embodiment, radiating patch 1211 is co-located with iris 1212.

FIG. 21 illustrates a cross section view of one embodiment of a physicalantenna aperture. The antenna aperture includes ground plane 1245, and ametal layer 1236 within iris layer 1233, which is included inreconfigurable resonator layer 1230. In one embodiment, the antennaaperture of FIG. 21 includes a plurality of tunable resonator/slots 1210of FIG. 20. Iris/slot 1212 is defined by openings in metal layer 1236. Afeed wave, such as feed wave 1205 of FIG. 20, may have a microwavefrequency compatible with satellite communication channels. The feedwave propagates between ground plane 1245 and resonator layer 1230.

Reconfigurable resonator layer 1230 also includes gasket layer 1232 andpatch layer 1231. Gasket layer 1232 is disposed between patch layer 1231and iris layer 1233. Note that in one embodiment, a spacer could replacegasket layer 1232. In one embodiment, iris layer 1233 is a printedcircuit board (“PCB”) that includes a copper layer as metal layer 1236.In one embodiment, iris layer 1233 is glass. Iris layer 1233 may beother types of substrates.

Openings may be etched in the copper layer to form slots 1212. In oneembodiment, iris layer 1233 is conductively coupled by a conductivebonding layer to another structure (e.g., a waveguide) in FIG. 21. Notethat in an embodiment the iris layer is not conductively coupled by aconductive bonding layer and is instead interfaced with a non-conductingbonding layer.

Patch layer 1231 may also be a PCB that includes metal as radiatingpatches 1211. In one embodiment, gasket layer 1232 includes spacers 1239that provide a mechanical standoff to define the dimension between metallayer 1236 and patch 1211. In one embodiment, the spacers are 75microns, but other sizes may be used (e.g., 3-200 mm). As mentionedabove, in one embodiment, the antenna aperture of FIG. 21 includesmultiple tunable resonator/slots, such as tunable resonator/slot 1210includes patch 1211, liquid crystal 1213, and iris 1212 of FIG. 20. Thechamber for liquid crystal 1213 is defined by spacers 1239, iris layer1233 and metal layer 1236. When the chamber is filled with liquidcrystal, patch layer 1231 can be laminated onto spacers 1239 to sealliquid crystal within resonator layer 1230.

A voltage between patch layer 1231 and iris layer 1233 can be modulatedto tune the liquid crystal in the gap between the patch and the slots(e.g., tunable resonator/slot 1210). Adjusting the voltage across liquidcrystal 1213 varies the capacitance of a slot (e.g., tunableresonator/slot 1210). Accordingly, the reactance of a slot (e.g.,tunable resonator/slot 1210) can be varied by changing the capacitance.The resonant frequency of slot 1210 also changes according to theequation f=½π√{right arrow over (LC)}, where f is the resonant frequencyof slot 1210 and L and C are the inductance and capacitance of slot1210, respectively. The resonant frequency of slot 1210 affects theenergy radiated from feed wave 1205 propagating through the waveguide.As an example, if feed wave 1205 is 20 GHz, the resonant frequency of aslot 1210 may be adjusted (by varying the capacitance) to 17 GHz so thatthe slot 1210 couples substantially no energy from feed wave 1205. Or,the resonant frequency of a slot 1210 may be adjusted to 20 GHz so thatthe slot 1210 couples energy from feed wave 1205 and radiates thatenergy into free space. Although the examples given are binary (fullyradiating or not radiating at all), full gray scale control of thereactance, and therefore the resonant frequency of slot 1210 is possiblewith voltage variance over a multi-valued range. Hence, the energyradiated from each slot 1210 can be finely controlled so that detailedholographic diffraction patterns can be formed by the array of tunableslots.

In one embodiment, tunable slots in a row are spaced from each other byλ/5. Other spacings may be used. In one embodiment, each tunable slot ina row is spaced from the closest tunable slot in an adjacent row by λ/2,and, thus, commonly oriented tunable slots in different rows are spacedby λ/4, though other spacings are possible (e.g., λ/5, λ/6.3). Inanother embodiment, each tunable slot in a row is spaced from theclosest tunable slot in an adjacent row by λ/3.

Embodiments use reconfigurable metamaterial technology, such asdescribed in U.S. patent application Ser. No. 14/550,178, entitled“Dynamic Polarization and Coupling Control from a SteerableCylindrically Fed Holographic Antenna”, filed Nov. 21, 2014 and U.S.patent application Ser. No. 14/610,502, entitled “Ridged Waveguide FeedStructures for Reconfigurable Antenna”, filed Jan. 30, 2015.

FIGS. 22A-D illustrate one embodiment of the different layers forcreating the slotted array. The antenna array includes antenna elementsthat are positioned in rings, such as the example rings shown in FIG.18. Note that in this example the antenna array has two different typesof antenna elements that are used for two different types of frequencybands.

FIG. 22A illustrates a portion of the first iris board layer withlocations corresponding to the slots. Referring to FIG. 22A, the circlesare open areas/slots in the metallization in the bottom side of the irissubstrate, and are for controlling the coupling of elements to the feed(the feed wave). Note that this layer is an optional layer and is notused in all designs. FIG. 22B illustrates a portion of the second irisboard layer containing slots. FIG. 22C illustrates patches over aportion of the second iris board layer. FIG. 22D illustrates a top viewof a portion of the slotted array.

FIG. 23 illustrates a side view of one embodiment of a cylindrically fedantenna structure. The antenna produces an inwardly travelling waveusing a double layer feed structure (i.e., two layers of a feedstructure). In one embodiment, the antenna includes a circular outershape, though this is not required. That is, non-circular inwardtravelling structures can be used. In one embodiment, the antennastructure in FIG. 23 includes a coaxial feed, such as, for example,described in U.S. Publication No. 2015/0236412, entitled “DynamicPolarization and Coupling Control from a Steerable Cylindrically FedHolographic Antenna”, filed on Nov. 21, 2014.

Referring to FIG. 23, a coaxial pin 1601 is used to excite the field onthe lower level of the antenna. In one embodiment, coaxial pin 1601 is a50Ω coax pin that is readily available. Coaxial pin 1601 is coupled(e.g., bolted) to the bottom of the antenna structure, which isconducting ground plane 1602.

Separate from conducting ground plane 1602 is interstitial conductor1603, which is an internal conductor. In one embodiment, conductingground plane 1602 and interstitial conductor 1603 are parallel to eachother. In one embodiment, the distance between ground plane 1602 andinterstitial conductor 1603 is 0.1-0.15″. In another embodiment, thisdistance may be λ/2, where λ is the wavelength of the travelling wave atthe frequency of operation.

Ground plane 1602 is separated from interstitial conductor 1603 via aspacer 1604. In one embodiment, spacer 1604 is a foam or air-likespacer. In one embodiment, spacer 1604 comprises a plastic spacer.

On top of interstitial conductor 1603 is dielectric layer 1605. In oneembodiment, dielectric layer 1605 is plastic. The purpose of dielectriclayer 1605 is to slow the travelling wave relative to free spacevelocity. In one embodiment, dielectric layer 1605 slows the travellingwave by 30% relative to free space. In one embodiment, the range ofindices of refraction that are suitable for beam forming are 1.2-1.8,where free space has by definition an index of refraction equal to 1.Other dielectric spacer materials, such as, for example, plastic, may beused to achieve this effect. Note that materials other than plastic maybe used as long as they achieve the desired wave slowing effect.Alternatively, a material with distributed structures may be used asdielectric 1605, such as periodic sub-wavelength metallic structuresthat can be machined or lithographically defined, for example.

An RF-array 1606 is on top of dielectric 1605. In one embodiment, thedistance between interstitial conductor 1603 and RF-array 1606 is0.1-0.15″. In another embodiment, this distance may be λ_(eff)/2, whereλ_(eff) is the effective wavelength in the medium at the designfrequency.

The antenna includes sides 1607 and 1608. Sides 1607 and 1608 are angledto cause a travelling wave feed from coax pin 1601 to be propagated fromthe area below interstitial conductor 1603 (the spacer layer) to thearea above interstitial conductor 1603 (the dielectric layer) viareflection. In one embodiment, the angle of sides 1607 and 1608 are at45° angles. In an alternative embodiment, sides 1607 and 1608 could bereplaced with a continuous radius to achieve the reflection. While FIG.23 shows angled sides that have angle of 45 degrees, other angles thataccomplish signal transmission from lower level feed to upper level feedmay be used. That is, given that the effective wavelength in the lowerfeed will generally be different than in the upper feed, some deviationfrom the ideal 45° angles could be used to aid transmission from thelower to the upper feed level. For example, in another embodiment, the45° angles are replaced with a single step. The steps on one end of theantenna go around the dielectric layer, interstitial the conductor, andthe spacer layer. The same two steps are at the other ends of theselayers.

In operation, when a feed wave is fed in from coaxial pin 1601, the wavetravels outward concentrically oriented from coaxial pin 1601 in thearea between ground plane 1602 and interstitial conductor 1603. Theconcentrically outgoing waves are reflected by sides 1607 and 1608 andtravel inwardly in the area between interstitial conductor 1603 and RFarray 1606. The reflection from the edge of the circular perimetercauses the wave to remain in phase (i.e., it is an in-phase reflection).The travelling wave is slowed by dielectric layer 1605. At this point,the travelling wave starts interacting and exciting with elements in RFarray 1606 to obtain the desired scattering.

To terminate the travelling wave, a termination 1609 is included in theantenna at the geometric center of the antenna. In one embodiment,termination 1609 comprises a pin termination (e.g., a 50Ω pin). Inanother embodiment, termination 1609 comprises an RF absorber thatterminates unused energy to prevent reflections of that unused energyback through the feed structure of the antenna. These could be used atthe top of RF array 1606.

FIG. 24 illustrates another embodiment of the antenna system with anoutgoing wave. Referring to FIG. 24, two ground planes 1610 and 1611 aresubstantially parallel to each other with a dielectric layer 1612 (e.g.,a plastic layer, etc.) in between ground planes. RF absorbers 1619(e.g., resistors) couple the two ground planes 1610 and 1611 together. Acoaxial pin 1615 (e.g., 50Ω) feeds the antenna. An RF array 1616 is ontop of dielectric layer 1612 and ground plane 1611.

In operation, a feed wave is fed through coaxial pin 1615 and travelsconcentrically outward and interacts with the elements of RF array 1616.

The cylindrical feed in both the antennas of FIGS. 23 and 24 improvesthe service angle of the antenna. Instead of a service angle of plus orminus forty-five degrees azimuth (±45° Az) and plus or minus twenty-fivedegrees elevation (±25° El), in one embodiment, the antenna system has aservice angle of seventy-five degrees (75°) from the bore sight in alldirections. As with any beam forming antenna comprised of manyindividual radiators, the overall antenna gain is dependent on the gainof the constituent elements, which themselves are angle-dependent. Whenusing common radiating elements, the overall antenna gain typicallydecreases as the beam is pointed further off bore sight. At 75 degreesoff bore sight, significant gain degradation of about 6 dB is expected.

Embodiments of the antenna having a cylindrical feed solve one or moreproblems. These include dramatically simplifying the feed structurecompared to antennas fed with a corporate divider network and thereforereducing total required antenna and antenna feed volume; decreasingsensitivity to manufacturing and control errors by maintaining high beamperformance with coarser controls (extending all the way to simplebinary control); giving a more advantageous side lobe pattern comparedto rectilinear feeds because the cylindrically oriented feed wavesresult in spatially diverse side lobes in the far field; and allowingpolarization to be dynamic, including allowing left-hand circular,right-hand circular, and linear polarizations, while not requiring apolarizer.

Array of Wave Scattering Elements

RF array 1606 of FIG. 23 and RF array 1616 of FIG. 24 include a wavescattering subsystem that includes a group of patch antennas (e.g.,surface scatterers) that act as radiators. This group of patch antennascomprises an array of scattering metamaterial elements.

In one embodiment, each scattering element in the antenna system is partof a unit cell that consists of a lower conductor, a dielectricsubstrate and an upper conductor that embeds a complementary electricinductive-capacitive resonator (“complementary electric LC” or “CELL”)that is etched in or deposited onto the upper conductor.

In one embodiment, a liquid crystal (LC) is injected in the gap aroundthe scattering element. Liquid crystal is encapsulated in each unit celland separates the lower conductor associated with a slot from an upperconductor associated with its patch. Liquid crystal has a permittivitythat is a function of the orientation of the molecules comprising theliquid crystal, and the orientation of the molecules (and thus thepermittivity) can be controlled by adjusting the bias voltage across theliquid crystal. Using this property, the liquid crystal acts as anon/off switch for the transmission of energy from the guided wave to theCELC. When switched on, the CELC emits an electromagnetic wave like anelectrically small dipole antenna.

Controlling the thickness of the LC increases the beam switching speed.A fifty percent (50%) reduction in the gap between the lower and theupper conductor (the thickness of the liquid crystal) results in afourfold increase in speed. In another embodiment, the thickness of theliquid crystal results in a beam switching speed of approximatelyfourteen milliseconds (14 ms). In one embodiment, the LC is doped in amanner well-known in the art to improve responsiveness so that a sevenmillisecond (7 ms) requirement can be met.

The CELC element is responsive to a magnetic field that is appliedparallel to the plane of the CELC element and perpendicular to the CELCgap complement. When a voltage is applied to the liquid crystal in themetamaterial scattering unit cell, the magnetic field component of theguided wave induces a magnetic excitation of the CELC, which, in turn,produces an electromagnetic wave in the same frequency as the guidedwave.

The phase of the electromagnetic wave generated by a single CELC can beselected by the position of the CELC on the vector of the guided wave.Each cell generates a wave in phase with the guided wave parallel to theCELC. Because the CELCs are smaller than the wave length, the outputwave has the same phase as the phase of the guided wave as it passesbeneath the CELC.

In one embodiment, the cylindrical feed geometry of this antenna systemallows the CELC elements to be positioned at forty-five-degree (45°)angles to the vector of the wave in the wave feed. This position of theelements enables control of the polarization of the free space wavegenerated from or received by the elements. In one embodiment, the CELCsare arranged with an inter-element spacing that is less than afree-space wavelength of the operating frequency of the antenna. Forexample, if there are four scattering elements per wavelength, theelements in the 30 GHz transmit antenna will be approximately 2.5 mm(i.e., ¼th the 10 mm free-space wavelength of 30 GHz).

In one embodiment, the CELCs are implemented with patch antennas thatinclude a patch co-located over a slot with liquid crystal between thetwo. In this respect, the metamaterial antenna acts like a slotted(scattering) wave guide. With a slotted wave guide, the phase of theoutput wave depends on the location of the slot in relation to theguided wave.

Cell Placement

In one embodiment, the antenna elements are placed on the cylindricalfeed antenna aperture in a way that allows for a systematic matrix drivecircuit. The placement of the cells includes placement of thetransistors for the matrix drive. FIG. 25 illustrates one embodiment ofthe placement of matrix drive circuitry with respect to antennaelements. Referring to FIG. 25, row controller 1701 is coupled totransistors 1711 and 1712, via row select signals Row1 and Row2,respectively, and column controller 1702 is coupled to transistors 1711and 1712 via column select signal Column1. Transistor 1711 is alsocoupled to antenna element 1721 via connection to patch 1731, whiletransistor 1712 is coupled to antenna element 1722 via connection topatch 1732.

In an initial approach to realize matrix drive circuitry on thecylindrical feed antenna with unit cells placed in a non-regular grid,two steps are performed. In the first step, the cells are placed onconcentric rings and each of the cells is connected to a transistor thatis placed beside the cell and acts as a switch to drive each cellseparately. In the second step, the matrix drive circuitry is built inorder to connect every transistor with a unique address as the matrixdrive approach requires. Because the matrix drive circuit is built byrow and column traces (similar to LCDs) but the cells are placed onrings, there is no systematic way to assign a unique address to eachtransistor. This mapping problem results in very complex circuitry tocover all the transistors and leads to a significant increase in thenumber of physical traces to accomplish the routing. Because of the highdensity of cells, those traces disturb the RF performance of the antennadue to coupling effect. Also, due to the complexity of traces and highpacking density, the routing of the traces cannot be accomplished bycommercially available layout tools.

In one embodiment, the matrix drive circuitry is predefined before thecells and transistors are placed. This ensures a minimum number oftraces that are necessary to drive all the cells, each with a uniqueaddress. This strategy reduces the complexity of the drive circuitry andsimplifies the routing, which subsequently improves the RF performanceof the antenna.

More specifically, in one approach, in the first step, the cells areplaced on a regular rectangular grid composed of rows and columns thatdescribe the unique address of each cell. In the second step, the cellsare grouped and transformed to concentric circles while maintainingtheir address and connection to the rows and columns as defined in thefirst step. A goal of this transformation is not only to put the cellson rings but also to keep the distance between cells and the distancebetween rings constant over the entire aperture. In order to accomplishthis goal, there are several ways to group the cells.

In one embodiment, a TFT package is used to enable placement and uniqueaddressing in the matrix drive. FIG. 26 illustrates one embodiment of aTFT package. Referring to FIG. 26, a TFT and a hold capacitor 1803 isshown with input and output ports. There are two input ports connectedto traces 1801 and two output ports connected to traces 1802 to connectthe TFTs together using the rows and columns. In one embodiment, the rowand column traces cross in 90° angles to reduce, and potentiallyminimize, the coupling between the row and column traces. In oneembodiment, the row and column traces are on different layers.

An Example of a Full Duplex Communication System

In another embodiment, the combined antenna apertures are used in a fullduplex communication system. FIG. 27 is a block diagram of an embodimentof a communication system having simultaneous transmit and receivepaths. While only one transmit path and one receive path are shown, thecommunication system may include more than one transmit path and/or morethan one receive path.

Referring to FIG. 27, antenna 1401 includes two spatially interleavedantenna arrays operable independently to transmit and receivesimultaneously at different frequencies as described above. In oneembodiment, antenna 1401 is coupled to diplexer 1445. The coupling maybe by one or more feeding networks. In one embodiment, in the case of aradial feed antenna, diplexer 1445 combines the two signals and theconnection between antenna 1401 and diplexer 1445 is a single broad-bandfeeding network that can carry both frequencies.

Diplexer 1445 is coupled to a low noise block down converter (LNB) 1427,which performs a noise filtering function and a down conversion andamplification function in a manner well-known in the art. In oneembodiment, LNB 1427 is in an out-door unit (ODU). In anotherembodiment, LNB 1427 is integrated into the antenna apparatus. LNB 1427is coupled to a modem 1460, which is coupled to computing system 1440(e.g., a computer system, modem, etc.).

Modem 1460 includes an analog-to-digital converter (ADC) 1422, which iscoupled to LNB 1427, to convert the received signal output from diplexer1445 into digital format. Once converted to digital format, the signalis demodulated by demodulator 1423 and decoded by decoder 1424 to obtainthe encoded data on the received wave. The decoded data is then sent tocontroller 1425, which sends it to computing system 1440.

Modem 1460 also includes an encoder 1430 that encodes data to betransmitted from computing system 1440. The encoded data is modulated bymodulator 1431 and then converted to analog by digital-to-analogconverter (DAC) 1432. The analog signal is then filtered by a BUC(up-convert and high pass amplifier) 1433 and provided to one port ofdiplexer 1445. In one embodiment, BUC 1433 is in an out-door unit (ODU).

Diplexer 1445 operating in a manner well-known in the art provides thetransmit signal to antenna 1401 for transmission.

Controller 1450 controls antenna 1401, including the two arrays ofantenna elements on the single combined physical aperture.

The communication system would be modified to include thecombiner/arbiter described above. In such a case, the combiner/arbiterafter the modem but before the BUC and LNB.

Note that the full duplex communication system shown in FIG. 27 has anumber of applications, including but not limited to, internetcommunication, vehicle communication (including software updating), etc.

There is a number of example embodiments described herein.

Example 1 is an antenna comprising: an array of antenna elements havingliquid crystal (LC); drive circuitry coupled to the array and having aplurality of drivers, each driver of the plurality of drivers coupled toan antenna element of the array and operable to apply a drive voltage tothe antenna element; and voltage correction logic coupled to the drivecircuitry to adjust drive voltages to compensate for an offset between afirst magnitude of a first voltage applied to the LC of each antennaelement during a first interval of drive polarity and a second magnitudeof a second voltage applied to the LC of said each antenna elementduring a second interval of drive polarity opposite the drive polarityof the first interval.

Example 2 is the antenna of example 1 that may optionally include thatthe voltage correction logic is operable to adjust the voltages to havethe offset between the first and second magnitudes to be substantiallyclose to zero.

Example 3 is the antenna of example 1 that may optionally include that acommon voltage is applied to antenna elements in the array, and furtherwherein the voltage correction logic is operable to adjust the commonvoltage to compensate for the offset.

Example 4 is the antenna of example 1 that may optionally include thatthe first and second intervals are positive and negative frames.

Example 5 is the antenna of example 4 that may optionally include thatthe voltage correction logic is operable to determine correctionvoltages based on an optical transmission difference between positiveand negative frames.

Example 6 is the antenna of example 5 that may optionally include one ormore optically transparent structures containing a test structure withoptical characteristics substantially equivalent to an antenna elementin the array and an observation window to obtain an optical response ofthe LC in the test structure for use in determining correction values.

Example 7 is the antenna of example 6 that may optionally include that acommon voltage is applied to antenna elements in the array, and furtherwherein the voltage correction circuitry is operable to adjust thecommon voltage for at least one antenna element based on null valuesproduced to optically null an RF element waveform in the one or moreoptically transparent structures.

Example 8 is the antenna of example 6 that may optionally include thatthe test structure is located outside a waveguide region associated witha waveguide that transfers RF energy to the antenna elements in thearray.

Example 9 is the antenna of example 6 that may optionally include thatthe test structure is located within the array.

Example 10 is the antenna of example 1 that may optionally include acontroller coupled to the drive circuitry to invert polarity of adifferential voltage applied on the LC of the antenna elementsperiodically.

Example 11 is a method comprising: (a) driving an element in an antenna;(b) observing a difference in optical transmission between positive andnegative frames; (c) adjusting a common voltage on the element to nullflicker; (d) creating new positive and negative frame voltages byadjusting old positive and negative frame voltages using the adjustedcommon voltage; (e) applying the new positive and negative framevoltages to the element; (f) checking for flicker with the element beingdriven by the new positive and negative frame voltages; and (g) usingthe new positive and negative frame voltages if an amount of flicker isbelow a threshold.

Example 12 is the method of example 11 that may optionally include thatthe element comprises a first test element and is driven at a first graylevel.

Example 13 is the method of example 12 that may optionally includerepeating operations (a)-(g) for a second gray level, the second graylevel not being the same as the first gray level.

Example 14 is the method of example 13 that may optionally includerepeating operations (a)-(g) for a plurality of gray levels other thanthe first gray level.

Example 15 is the method of example 11 that may optionally includeinterpolating correction values obtained from the first test element anda second test element to obtain a correction value for use with anantenna element located between the first and second test elements.

Example 16 is the method of example 11 that may optionally include thatthe threshold is a state in which flicker does not exist with theelement.

Example 17 is a non-transitory computer readable storage media havinginstructions stored thereupon which, when executed by a system having atleast a processor and a memory therein, cause the system to perform amethod comprising: (a) driving an element in an antenna; (b) observing adifference in optical transmission between positive and negative frames;(c) adjusting a common voltage on the element to null flicker; (d)creating new positive and negative frame voltages by adjusting oldpositive and negative frame voltages using the adjusted common voltage;(e) applying the new positive and negative frame voltages to theelement; (f) checking for flicker with the element being driven by thenew positive and negative frame voltages; and (g) using the new positiveand negative frame voltages if an amount of flicker is below athreshold.

Example 18 is the readable storage media of example 17 that mayoptionally include that the element comprises a first test element andis driven at a first gray level.

Example 19 is the readable storage media of example 18 that mayoptionally include that the method further comprises repeatingoperations (a)-(g) for a second gray level, the second gray level notbeing the same as the first gray level.

Example 20 is the readable storage media of example 19 that mayoptionally include that the method further comprises repeatingoperations (a)-(g) for a plurality of gray levels other than the firstgray level.

Example 21 is the readable storage media of example 17 that mayoptionally include that the method further comprises interpolatingcorrection values obtained from the first test element and a second testelement to obtain a correction value for use with an antenna elementlocated between the first and second test elements.

Example 22 is the readable storage media of example 17 that mayoptionally include that the threshold is a state in which flicker doesnot exist with the element.

Example 23 is a method comprising: obtaining an optical response of anantenna element of an antenna aperture; and correcting a differencebetween the positive and negative frames based on the obtained opticalresponse.

Example 24 is the method of example 23 that may optionally include thatthe optical response is measured using a test optical structure on theantenna aperture.

Some portions of the detailed descriptions above are presented in termsof algorithms and symbolic representations of operations on data bitswithin a computer memory. These algorithmic descriptions andrepresentations are the means used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of steps leading to a desiredresult. The steps are those requiring physical manipulations of physicalquantities. Usually, though not necessarily, these quantities take theform of electrical or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the following discussion,it is appreciated that throughout the description, discussions utilizingterms such as “processing” or “computing” or “calculating” or“determining” or “displaying” or the like, refer to the action andprocesses of a computer system, or similar electronic computing device,that manipulates and transforms data represented as physical(electronic) quantities within the computer system's registers andmemories into other data similarly represented as physical quantitieswithin the computer system memories or registers or other suchinformation storage, transmission or display devices.

The present invention also relates to apparatus for performing theoperations herein. This apparatus may be specially constructed for therequired purposes, or it may comprise a general-purpose computerselectively activated or reconfigured by a computer program stored inthe computer. Such a computer program may be stored in a computerreadable storage medium, such as, but is not limited to, any type ofdisk including floppy disks, optical disks, CD-ROMs, andmagnetic-optical disks, read-only memories (ROMs), random accessmemories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, or any typeof media suitable for storing electronic instructions, and each coupledto a computer system bus.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general-purposesystems may be used with programs in accordance with the teachingsherein, or it may prove convenient to construct more specializedapparatus to perform the required method steps. The required structurefor a variety of these systems will appear from the description below.In addition, the present invention is not described with reference toany particular programming language. It will be appreciated that avariety of programming languages may be used to implement the teachingsof the invention as described herein.

A machine-readable medium includes any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputer). For example, a machine-readable medium includes read onlymemory (“ROM”); random access memory (“RAM”); magnetic disk storagemedia; optical storage media; flash memory devices; etc.

Whereas many alterations and modifications of the present invention willno doubt become apparent to a person of ordinary skill in the art afterhaving read the foregoing description, it is to be understood that anyparticular embodiment shown and described by way of illustration is inno way intended to be considered limiting. Therefore, references todetails of various embodiments are not intended to limit the scope ofthe claims which in themselves recite only those features regarded asessential to the invention.

We claim:
 1. An antenna comprising: an array of antenna elements havingliquid crystal (LC); drive circuitry coupled to the array and having aplurality of drivers, each driver of the plurality of drivers coupled toan antenna element of the array and operable to apply a drive voltage tothe antenna element; and voltage correction logic coupled to the drivecircuitry to adjust drive voltages to compensate for an offset between afirst magnitude of a first voltage applied to the LC of each antennaelement during a first interval of drive polarity and a second magnitudeof a second voltage applied to the LC of said each antenna elementduring a second interval of drive polarity opposite the drive polarityof the first interval.
 2. The antenna defined in claim 1 wherein thevoltage correction logic is operable to adjust the voltages to have theoffset between the first and second magnitudes to be substantially closeto zero.
 3. The antenna defined in claim 1 wherein a common voltage isapplied to antenna elements in the array, and further wherein thevoltage correction logic is operable to adjust the common voltage tocompensate for the offset.
 4. The antenna defined in claim 1 wherein thefirst and second intervals are positive and negative frames.
 5. Theantenna defined in claim 4 wherein the voltage correction logic isoperable to determine correction voltages based on an opticaltransmission difference between positive and negative frames.
 6. Theantenna defined in claim 5 further comprising one or more opticallytransparent structures containing a test structure with opticalcharacteristics substantially equivalent to an antenna element in thearray and an observation window to obtain an optical response of the LCin the test structure for use in determining correction values.
 7. Theantenna defined in claim 6 wherein a common voltage is applied toantenna elements in the array, and further wherein the voltagecorrection circuitry is operable to adjust the common voltage for atleast one antenna element based on null values produced to opticallynull an RF element waveform in the one or more optically transparentstructures.
 8. The antenna defined in claim 6 wherein the test structureis located outside a waveguide region associated with a waveguide thattransfers RF energy to the antenna elements in the array.
 9. The antennadefined in claim 6 wherein the test structure is located within thearray.
 10. The antenna defined in claim 1 further comprising acontroller coupled to the drive circuitry to invert polarity of adifferential voltage applied on the LC of the antenna elementsperiodically.
 11. A method comprising: (a) driving an element in anantenna; (b) observing a difference in optical transmission betweenpositive and negative frames; (c) adjusting a common voltage on theelement to null flicker; (d) creating new positive and negative framevoltages by adjusting old positive and negative frame voltages using theadjusted common voltage; (e) applying the new positive and negativeframe voltages to the element; (f) checking for flicker with the elementbeing driven by the new positive and negative frame voltages; and (g)using the new positive and negative frame voltages if an amount offlicker is below a threshold.
 12. The method defined in claim 11 whereinthe element comprises a first test element and is driven at a first graylevel.
 13. The method defined in claim 12 further comprising repeatingoperations (a)-(g) for a second gray level, the second gray level notbeing the same as the first gray level.
 14. The method defined in claim13 further comprising repeating operations (a)-(g) for a plurality ofgray levels other than the first gray level.
 15. The method defined inclaim 11 further comprising interpolating correction values obtainedfrom the first test element and a second test element to obtain acorrection value for use with an antenna element located between thefirst and second test elements.
 16. The method defined in claim 11wherein the threshold is a state in which flicker does not exist withthe element.
 17. A non-transitory computer readable storage media havinginstructions stored thereupon which, when executed by a system having atleast a processor and a memory therein, cause the system to perform amethod comprising: (a) driving an element in an antenna; (b) observing adifference in optical transmission between positive and negative frames;(c) adjusting a common voltage on the element to null flicker; (d)creating new positive and negative frame voltages by adjusting oldpositive and negative frame voltages using the adjusted common voltage;(e) applying the new positive and negative frame voltages to theelement; (f) checking for flicker with the element being driven by thenew positive and negative frame voltages; and (g) using the new positiveand negative frame voltages if an amount of flicker is below athreshold.
 18. The computer readable storage media defined in claim 17wherein the element comprises a first test element and is driven at afirst gray level.
 19. The computer readable storage media defined inclaim 18 wherein the method further comprises repeating operations(a)-(g) for a second gray level, the second gray level not being thesame as the first gray level.
 20. The computer readable storage mediadefined in claim 19 wherein the method further comprises repeatingoperations (a)-(g) for a plurality of gray levels other than the firstgray level.
 21. The computer readable storage media defined in claim 17wherein the method further comprises interpolating correction valuesobtained from the first test element and a second test element to obtaina correction value for use with an antenna element located between thefirst and second test elements.
 22. The computer readable storage mediadefined in claim 17 wherein the threshold is a state in which flickerdoes not exist with the element.
 23. A method comprising: obtaining anoptical response of an antenna element of an antenna aperture; andcorrecting a difference between the positive and negative frames basedon the obtained optical response.
 24. The method defined in claim 23wherein the optical response is measured using a test optical structureon the antenna aperture.